Nitrogen fixation and growth of soybean as influenced by varying the methods of inoculation with Bradyrhizobium japonicum

Abstract

The effects of inoculating soil with a water suspension of Bradyrhizobium japonicum (i) at seeding, (ii) 7, or (iii) 14 days after planting (DAP), (iv) seed slurry inoculation and (v) seed slurry supplemented with postemergence inoculation of a water suspension of Bradyrhizobium at 7 or (vi) 14 DAP, on nodulation, N 2 fixation and yield of soybean (Glycine max. [L.] Merrill) were compared in the greenhouse. The ~SN isotope dilution technique was used to quantify N 2 fixed at flowering, early pod filling and physiological maturity stages (36, 52 and 70 DAP, respectively). On average, the water suspension inoculation formed the greatest number of nodules, and seed plus postemergence inoculation formed slightly more nodules than the seed-only inoculated plants (27, 19 and 12 nodules/plant respectively at physiological maturity). Seed slurry inoculation followed by postemergence inoculation at 14 DAP gave the highest nodule weight, with the plants fixing significantly more (P< 0.05) N 2 (125 mg N plant -~ or 56% N) than any other treatment (mean, 75 mg plant -1 or 35% N). However, the higher N 2 fixation was not translated into higher N or dry matter yields. Estimates of N 2 fixed by the postemergence Bradyrhizobium inoculations as well as plant yield were not significantly different from those of the seed slurry inoculation. Thus, delaying inoculation (e.g., by two weeks as in this study) did not reduce the symbiotic ability of soybean plants.

Optimisation of inoculation of Leucaena leucocephala and Acacia mangium with rhizobium under greenhouse conditions

“…However, until now these techniques were used without including several factors that can optimise inoculation. Experiments that were carried out with the help of many leguminous species did not take into account the effect of the method of inoculation, the size of the inoculum, the period of inoculation or the effects of the physiological stage of the bacterial strains on nodulation and biomass production [5]. Some of the key studies carried out on the inoculation of Acacia mangium and Leucaena leucocephala are summarised in Table I.…”

Relationship between nitrogen sources, germination and vigor of soybean seeds

“…However, even though promising, the information on the effects of the utilization of liquid carriers for the inoculant is less available, as pointed out by HAMMOUD (1981) and DANSO et al (1990), among others.…”

Assessment of potential sources of error in nitrogen fixation measurements by the nitrogen-15 isotope dilution technique

“…The data were derived from the study reported in detail in another paper (Danso et al, 1990), which examined the effects of various inoculation procedures on the growth and N 2 fixation in soybean (Glycine max. (L.) Merrill).…”

“…For easy reference, LSD comparisons were all presented in the Tables at the 0.05 level, but where the significance was at the 0.01 level, this is stated in the text. Since treatment effects have already been reported (Danso et al, 1990), statistical comparisons between inoculation treatments have been excluded from this paper.…”

“…This paper, which is based on data from another study (Danso et al, 1990) examines some controversial or doubtful aspects of the N-15 isotope dilution methodology (Fried and Middelboe, 1977;McAuliffe et al, 1958), and whether these significantly affect estimates of N 2 fixation in soybean or not.…”